Lubrication

(Please note the description below is based on the configuration of the current prototype activity and varies slightly from the drawings above.)

The S2S does not use its’ crankcase as its’ scavenge pump, this allows a conventional wet sump, crankshaft, rod and plain bearings to be used, enhancing durability and improving NVH over a typical two-stroke. The wet sump provides a reservoir of oil for cooling as well as lubrication. 

A constant film of oil is wiped onto the outside of the piston that runs from the top of the piston upright, under the ring in the piston top, to the bottom of the piston skirt. This un-interrupted film is possible because the piston and cylinder thrust quadrants are aligned with the piston uprights and are therefore never exposed to combustion. This allows the piston to operate in similar fashion to a crosshead, commonly used in huge marine and industrial engines when very long life is a requirement.

Before flowing out the bottom of the piston and returning to the crankcase, grooves in the surface of the uprights lead some oil to other areas needing lubrication; thrust sections, rings, seals and sealing plugs. Oil for the head seal can travel through a small hole in the piston upright, or directly to the seal from a galley in the head itself. 

Sealing 

A system of conventional rings, straight seals and joining plugs (such as used in the Wankel Rotary engine) and seal the S2S. 

A conventional ring is at the top of the piston; it scrapes oil from cylinder walls and seals the upper chamber and middle chamber for pumping purposes. 

Head seals are stationary in the head, pressed toward the inside of the piston upright by a backing spring. This is a bimetal seal, it's face is a softer material compatable with the piston, as it  seals on the piston upright. The upper and lower sides of the seal are harder material to cope with the slight shifting in the retaining groove. Its’ stationary location allows for flexible size and material and makes lubrication convenient. The inside surface of the piston upright does not contact the head. Piston fit is conventional cylinder bore to piston outer diameter. Enlargement of the gap due to wear  is taken up by the seal, without effecting piston/cylinder fit.

The vertical seals are housed in a groove the cylinder, making them stationary. To enhance sealing, an opposing groove is cut in the piston, so the seal fits closely in a groove in both the cylinder and piston. This close fit allows the seal to be more of a plug than a seal, no pressing action is required and therefore no backing spring is needed.

Lubrication of vertical seals is provided by hollow " C " shaped plugs, receiving oil from the upright quadrants and returning it through a small hole in the piston.  

Sealing the combustion chamber at the piston crown between the uprights is a conventional ring.  

At the bottom of the piston skirt is a conventional oil ring. By extending the vertical seals to join with this  ring the exhaust port(s) are isolated from the crankcase and from the two oil-streaming thrust quadrants aligned with the piston uprights. 

Rings are pinned to prevent rotation (standard two-stroke practice) and shallow notches on the face of the ring align with the vertical seals allowing them to mesh without contact.

Cooling 

The upper cylinder houses the upper (supercharger) and middle (scavenging) chambers, both intake cool fresh air, keeping the cylinder temperature inherently low. The walls of this cylinder are thinner, as the pressures are much lower, leaving extra space for cooling surfaces and aiding cooling. 

The head is cooled by air on its’ upper surface (which is the lower surface of the scavenge chamber) and conduction out of its’ ends to attached and/or joined cylinders. It may also be cooled by liquid pumped through interior passages, as its’ interior is unobstructed. 

The lower cylinder has a reduced thermal load because the piston uprights block half of the interior circumference. For this reason cooling would be easily accomplished by air or liquid methods. 

The piston has an additional heat burden as the inside surface of its’ uprights form a portion of the combustion chamber. As described earlier, oil is conveniently in constant flow down a channel on the backsides of the uprights, this oil absorbs combustion heat from the piston and uprights. Scavenge air also cools the uprights during the scavenge phase. The piston top while thin and lightweight represents a large area receiving a constant cool airflow. These factors taken together are expected to yield a cool running piston. 

Durability

Unlike conventional two-strokes the Super Two-stroke uses the same wet-sump, plain bearing crankshaft assembly as a four-stroke, a proven durable unit. Most engines burn off cylinder wall oil with each power stroke, allowing the cylinder to wear on the thrust side due to friction. The super two stroke thrust side cylinder walls are never exposed to combustion, insuring a constant oil film and less wear.